The present invention relates generally to disc brakes for vehicles and more particularly, to an electrically operated disc brake wherein a motor torque is used to produce a braking force.
A known electrically operated disc brake includes a caliper body within which a ball/ramp mechanism is arranged to convert rotary motion of an electric motor to linear motion and transmit the linear motion to a piston. The piston is advanced in response to operation of the electric motor so as to urge a pair of friction pads against opposite sides of a disc rotor to brake the rotor.
In such an electrically operated disc brake, the ball/ramp mechanism as well as the electric motor is subject to malfunction in the even that water and dust accidentally enters within the caliper body. To this end, attempts have been made to provide a dust boot between the caliper body and one end of the piston located adjacent to the disc rotor.
The dust boot is, however, exposed to severe environment during operation of the vehicle and is susceptible to damage due to contact with stones and various other obstacles.
A seal may be disposed between the cylindrical wall of the piston and the caliper body. The seal and the duct boot may cooperate together to effectively protect the ball/ramp mechanism from damage. However, such a seal can not be used with a pad wear adjusting mechanism generally used in the electrically operated disc brake. The pad wear adjusting mechanism is operable to threadably move the piston relative to an axially movable member of the ball/ram mechanism in response to the amount of pad wear (see, for example, Japanese laid-open patent publication No. 2000-145843). The piston has a threaded section along its full length. This arrangement inhibits the use of the seal between the piston and the caliper body.
Accordingly, it is an object of the present invention to provide an electrically operated disc brake which ensures safe operation of a ball/ramp mechanism and which permits the use of a dual seal arrangement to significantly increase the useful life of the electrically operated disc brake.